Many isolates of SIV have been identified and SIVPBj14 has been well characterized and studied both in vitro and in vivo. This particular viral isolate is generally considered to be more pathogenic than other strains such as SIVmne and SIVmac251. Because of its pathogenic nature, SIVPBj14 may be suitable for antiretroviral studies in macaques since the effects of drug therapy can be monitored on both virology and pathogenesis. For these reasons, we produced a cell-free uncloned SIVPBj14 virus stock for inoculations and antiretroviral studies in the macaque model. This virus stock was titrated in macaques to determine the 100% infectious dose. Further titrations will be unnecessary, and all future antiretroviral drug studies will use the same viral inoculum for the macaques. In 1998 eight macaques inoculated with SIVPBj14 remained in a long-term follow-up study. FUNDING NIH contract AI65311 and NIH grant RR00166.